The invention concerns a method for detecting a first baseband signal sent by a first sending station via an air interface to a first radio station of a radio communications system as well as a respective first radio station and a respective radio communications system.
In recent years, much research has been conducted on multiple-input multiple-output (MIMO) systems and a large number of algorithms have been developed, mostly for wireless LAN (Local Area Network) and partly for cellular radio communication systems. They have been proposed to support a single terminal with multiple antennas (as in MIMO WLAN or HSDPA) or to support multiple terminals, both from a single base station with multiple antennas (which is called space-division multiple access, SDMA). These approaches can partly be used to cancel interference provided that there are unused degrees of freedom, i.e., less terminal antennas than base station antennas.
When for instance in the up-link terminals and base stations are well synchronized and the channels between all terminals and base stations are known, the multi-user multi cell scenario can be regarded as a generalized MIMO channel, where terminal antennas form the inputs and the antennas at multiple base stations the outputs.
It is well known under the term service area concept that joint transmission and detection of user signals controlled by a central unit can cancel the interference within a service area—which has two or more base stations—completely. In the ideal case of so-called “writing on dirty paper” inter-cell interference can be cancelled without any performance degradation.
The centralized service area concept suffers from high complexity. In principle, the larger a service area the larger the complexity and, of course, the more interference can be cancelled inside the service area. Previous investigations showed however that the service area concept works fine inside a service area but the same problems as for single cells without coordination arise now on a larger scale at the boundaries of the service area.
The service area concept requires interconnections with high data rate to transport the signals from all base stations to one central unit where a computationally complex problem must be solved. Note that the complexity rises at least with the third order of the number of base stations involved. It is not taken into account that at some locations only little interference may be present. This is handled in the same manner as high interference.
In X. Tao, C. Tang, Z. Dai, X. Xu, B. Liu, P. Zhang “Capacity Analysis for a Generalized Distributed Antenna Architecture for Beyond 3G Systems” in Proc. VTC Spring 2005, Stockholm, Sweden, Vol. 5, pp. 3193-3196, a sliding group-cell concept has been proposed in which a central unit has been used. When a terminal moves through a service area, the central unit forms subgroups of cells for joint transmission and detection in order to reduce the complexity. When the terminal is mobile, the position is tracked and new subgroups are formed.
In A. Vanelli-Coralli, R. Padovani, J. Hou, J. E. Smee, “Capacity of Cell Clusters with Coordinated Processing”, USCD Inaugural workshop on Information theory and it's applications”, La Jolla, Calif., Feb. 6-10, 2006, the service area concept is denoted as scenario C.